How a differential pressure transmitter is used to measure the flow of a gas or liquid in a closed pipe.
This video guide explains the different types of primary elements used to measure flow and how they produce a differential pressure which can then be converted to a linear measurement of flow from calculating the square root of the pressure. It also covers the ways to install a DP transmitter on different types of media flow.
Inside a Differential Pressure Transmitter
Explanatory video of how a typical process differential pressure transmitter works using a cutaway Rosemount 3051 pressure transmitter.
This overview of the workings of a DP cell, guides you through the various mechanical components such as the functional purpose of the process isolation diaphragms, the oil fill and the capacitance sensing element.
This overview of the workings of a DP cell, guides you through the various mechanical components such as the functional purpose of the process isolation diaphragms, the oil fill and the capacitance sensing element.
Determining the Linearity Error of a Pressure Transducer
This type of error refers to the straightness of all points measured over the full range of the pressure transducer. It is some times quoted as an alternative to accuracy, but is mostly incorporated into an overall accuracy with other parameters such as hysteresis and repeatability.
To calculate the linearity of a pressure transducer, first you must collect the measurement data. The typical way to do this is to apply pressure at fixed intervals from zero to full scale pressure and measure the output at each pressure set-point. The more pressure points there are, the more accurate will be the linearity calculation. The minimum number of points to determine linearity is 3 points and there is no limit on the maximum, but 5-10 points is typical for one set of pressure points.
To calculate the linearity of a pressure transducer, first you must collect the measurement data. The typical way to do this is to apply pressure at fixed intervals from zero to full scale pressure and measure the output at each pressure set-point. The more pressure points there are, the more accurate will be the linearity calculation. The minimum number of points to determine linearity is 3 points and there is no limit on the maximum, but 5-10 points is typical for one set of pressure points.
Hysteresis Error Calculation for a Pressure Transducer
This relates to the mechanical hysteresis of the sensing diaphragm where the electrical signal output varies depending on whether the pressure has been increasing or decreasing prior to the measurement.
The way that a pressure transducer is checked for hysteresis is to apply pressure from zero to full scale pressure, typically stopping without overshoot at 5 equally spaced steps in pressure to measure the value. Then repeat the procedure in the opposite direction from full scale to zero pressure.
The way that a pressure transducer is checked for hysteresis is to apply pressure from zero to full scale pressure, typically stopping without overshoot at 5 equally spaced steps in pressure to measure the value. Then repeat the procedure in the opposite direction from full scale to zero pressure.
Digital Output Square Root Extraction Formula and Tables
Square root extraction signals are used to simplify closed pipe liquid or gas flow calculations and to improve resolution of the non-linear signal when converted to a flow reading.
The output from a Modbus 12 bit count can be transformed in the following ways:
A linear digital output signal of 0 to 4096 steps can be converted to a non-linear sq rt extraction by applying the following formula or table:
The output from a Modbus 12 bit count can be transformed in the following ways:
A linear digital output signal of 0 to 4096 steps can be converted to a non-linear sq rt extraction by applying the following formula or table:
Advantages and Disadvantages of using a 4 to 20 mA Signal
A 4-20mA current signal has become very popular for many applications beyond it's original intended purpose in the process industry. It is now used throughout industry as the preferred measurement and control signal for many different types of systems.
Despite the popularity of the 4-20mA signal, it is not the best solution for every application and here are some of the 'for' and 'against' reasons for determining whether it is the right type of signal for your application.
Despite the popularity of the 4-20mA signal, it is not the best solution for every application and here are some of the 'for' and 'against' reasons for determining whether it is the right type of signal for your application.
How to Quickly find a Manufacturer's PDF Product Data Sheet
A pdf (Public Document Format) file is the most reliable and authoritive document to find if you are looking to view the manufacturer's specification for a particular product.
A pdf document has become the De facto standard for the majority of manufacturer's marketing departments because it enables them to better control the distribution of the published specification for their product. The pdf file format is not easily editable, the content is always rendered the same way no matter what device it is viewed on and most computer users can open the files with free to download reader software such as Adobe Reader.
A pdf document has become the De facto standard for the majority of manufacturer's marketing departments because it enables them to better control the distribution of the published specification for their product. The pdf file format is not easily editable, the content is always rendered the same way no matter what device it is viewed on and most computer users can open the files with free to download reader software such as Adobe Reader.
Why do Pressure Calibration Certificates show Rising and Falling Results?
When looking at a calibration certificate you will notice that the calibration points are set out in the order they were recorded as one set of rising results followed by a set of falling results.
The majority of pressure measurement equipment relies on the flexing of a mechanical component such as a metal diaphragm or a Bourdon Tube to sense a change in pressure. If you compare increasing pressure points to decreasing pressure points you will discover that the readings do not match exactly. This is due to Mechanical Hysteresis and the amount of error will vary depending on the amplitude of the cycle of pressure.
The majority of pressure measurement equipment relies on the flexing of a mechanical component such as a metal diaphragm or a Bourdon Tube to sense a change in pressure. If you compare increasing pressure points to decreasing pressure points you will discover that the readings do not match exactly. This is due to Mechanical Hysteresis and the amount of error will vary depending on the amplitude of the cycle of pressure.
Not Reading Zero when Pressure is Vented to Atmosphere
It is not unusual for a pressure measurement device to read slightly above or below zero with no pressure applied. The zero offset tolerance for a device is often incorporated into the accuracy statement or shown as a separate spec on the product data sheet.
When a gauge reference pressure instrument is first installed it should read very close to zero when measuring ambient air pressure. Some devices such as analogue output sensor, may have a small zero offset because it does not have sufficient fine adjustment to set the zero reading exactly. If there is a zero offset at zero pressure on a new device, it should be relatively small compared to the full measurement range.
When a gauge reference pressure instrument is first installed it should read very close to zero when measuring ambient air pressure. Some devices such as analogue output sensor, may have a small zero offset because it does not have sufficient fine adjustment to set the zero reading exactly. If there is a zero offset at zero pressure on a new device, it should be relatively small compared to the full measurement range.
What is a mV/V Output Sensitivity?
It is an electrical signal which is proportional to the applied excitation voltage and is also referred to as a ratio-metric or strain gauge output.
This type of output signal is produced by a wheatstone bridge strain gauge transducer which converts imbalance in bridge resistance generated by an applied force / load to a voltage drop between two opposite corners of the Wheatstone bridge circuit.
For a given fixed force, load or pressure, the voltage drop across two opposite corners of the circuit will is linearly proportional to the voltage supplied between the other two corners of the circuit. In a circuit diagram the wheatstone bridge is usually shown as four resistors representing the strain gauges, joined together in a diamond shape.
This type of output signal is produced by a wheatstone bridge strain gauge transducer which converts imbalance in bridge resistance generated by an applied force / load to a voltage drop between two opposite corners of the Wheatstone bridge circuit.
For a given fixed force, load or pressure, the voltage drop across two opposite corners of the circuit will is linearly proportional to the voltage supplied between the other two corners of the circuit. In a circuit diagram the wheatstone bridge is usually shown as four resistors representing the strain gauges, joined together in a diamond shape.
How to Connect a 4-20mA Current Loop Pressure Transmitter
All devices connected to make up a 4 to 20 milliamp current loop are connected in series.
The devices that are typically connected together include:
The devices that are typically connected together include:
- Pressure Transmitter
- Input Device to accept the signal from the Pressure Transmitter such as a Programmable Logic Controller (PLC), Controller, Panel Meter, Analog to Digital Converter (ADC) or Signal Conditioning Unit (SCU)
- Sensor Power Supply to power the Pressure Transmitter such as a Programmable Power Supply unit, DC Power Supply Unit (PSU), AC/DC Voltage Regulated Transformer or a DC Battery
Using Data Logging Equipment to Record and Analyze Measurement Readings
The primary function of a data logger is to create a record of measurements over a period of time at preset intervals.
Datalogging is used to record measurement in many areas of research and industry such as material performance testing, environmental monitoring, quality auditing, scientific experimentation and design proofing.
The main advantage of recording measurements using a data recorder is that it eliminates the errors and time spent writing down or typing in measurement results.
Datalogging is used to record measurement in many areas of research and industry such as material performance testing, environmental monitoring, quality auditing, scientific experimentation and design proofing.
The main advantage of recording measurements using a data recorder is that it eliminates the errors and time spent writing down or typing in measurement results.
Symptons and Causes of Damage to Pressure Transducer Diaphragms
It is possible to view part of the diaphragm on most pressure transducers and some which are completely exposed such as flush diaphragms are particular vulnerable to mechanical damage.
The first sign of damage may not actually be that detectable to the eye, instead it may show up as a small zero setting offset on the output signal. In some cases the damage maybe so severe that the diaphragm has completely ruptured compromising pressure containment or it is touching an internal component causing mechanical interference or an electrical short/open circuit.
The first sign of damage may not actually be that detectable to the eye, instead it may show up as a small zero setting offset on the output signal. In some cases the damage maybe so severe that the diaphragm has completely ruptured compromising pressure containment or it is touching an internal component causing mechanical interference or an electrical short/open circuit.
Explanations for Measurement Accuracy Specifications
The way accuracy is defined for pressure instruments on technical data sheets can vary significantly across manufacturers and product types.
There are many contributing error factors which go into a total uncertainty calculation and the proportion contributed by each one will be different from one measurement technology to another.
There are many contributing error factors which go into a total uncertainty calculation and the proportion contributed by each one will be different from one measurement technology to another.
ATEX Classifications Glossary for products used in Explosive Atmospheres
Explanations for product markings found on ATEX approved equipment. ATEX is the regulatory directive for the design, installation and use of products in environments where there is a potential explosion risk from flammable gases or dust that are or could be present in the surrounding air.
For more in-depth information on the ATEX directive we suggest you visit the UK Health and Safety Executive or the European Union Commission. To get a product ATEX approved we suggest contacting Baseefa or SIRA in the UK.
For more in-depth information on the ATEX directive we suggest you visit the UK Health and Safety Executive or the European Union Commission. To get a product ATEX approved we suggest contacting Baseefa or SIRA in the UK.
Practical uses of Atmospheric Pressure Measurement
The measurement of ambient air pressure is carried out in many applications throughout research and industry.
The most well known use is as a barometer for weather monitoring but there are a number of other measurements that incorporate barometric pressure as well, some of the most common are explained below.
The most well known use is as a barometer for weather monitoring but there are a number of other measurements that incorporate barometric pressure as well, some of the most common are explained below.
Measuring Suction and Vacuum Pressure
Explanations for technical queries relating to measuring negative gauge and absolute pressures in the vacuum range.
How is suction pressure measured?
Use a gauge reference pressure measuring device with a range scaled in the negative direction. The zero to full scale range will depend on the maximum suction pressure expected.
How is a vacuum measured?
A vacuum is any pressure that is below atmospheric pressure. A vacuum can be measured using an absolute pressure sensing device. Zero absolute pressure is a perfect vacuum, the higher the absolute pressure the lower the vacuum.
How is suction pressure measured?
Use a gauge reference pressure measuring device with a range scaled in the negative direction. The zero to full scale range will depend on the maximum suction pressure expected.
How is a vacuum measured?
A vacuum is any pressure that is below atmospheric pressure. A vacuum can be measured using an absolute pressure sensing device. Zero absolute pressure is a perfect vacuum, the higher the absolute pressure the lower the vacuum.
Questions often asked about Pressure Calibration
Explanations for questions asked about pressure calibration techniques and terminology.
How often should you calibrate?
There is no recommended fixed period of time for re-calibrating pressure instruments since they all differ from each other in how accurately they measure pressure and how stable they are over time. Ideally if pressure measurement performance is critical to your business operation it is advisable to calibrate all pressure measuring devices as frequently as possible. Once at least 3 sets of calibration test results has been collected, the data can be compared to determine whether the re-calibration cycle can be lengthened.
How often should you calibrate?
There is no recommended fixed period of time for re-calibrating pressure instruments since they all differ from each other in how accurately they measure pressure and how stable they are over time. Ideally if pressure measurement performance is critical to your business operation it is advisable to calibrate all pressure measuring devices as frequently as possible. Once at least 3 sets of calibration test results has been collected, the data can be compared to determine whether the re-calibration cycle can be lengthened.
Using Hydrostatic Pressure Transducers for Measuring Fluid Level
There are a number of methods and technologies for measuring the level of a fluid, all of them have advantages and disadvantages depending on the installation. Measuring hydrostatically is an accurate and convenient technique for determining fluid height or volume.
Hydrostatic pressure transducers are very similar to pneumatic or hydraulic pressure transducers in the way pressure is measured, but there are some differences which are specific to liquid level measurement.
Hydrostatic pressure transducers are very similar to pneumatic or hydraulic pressure transducers in the way pressure is measured, but there are some differences which are specific to liquid level measurement.
Absolute Pressure Measurement Frequently Asked Questions
Explanations for queries related to sensors and instrumentation used for measuring pressure with an absolute zero vacuum reference.
Why is it called "absolute" pressure?
It refers to the fact that the reference is fixed at the lowest possible pressure, a perfect vacuum, so that the pressure reading is always compared to an unconditional and static reference.
How do you convert a gauge pressure to an absolute one?
If you know the local ambient air pressure, the absolute pressure can be determined by adding it to the gauge pressure, i.e. P (abs) = P (atm) + P (gauge).
Why is it called "absolute" pressure?
It refers to the fact that the reference is fixed at the lowest possible pressure, a perfect vacuum, so that the pressure reading is always compared to an unconditional and static reference.
How do you convert a gauge pressure to an absolute one?
If you know the local ambient air pressure, the absolute pressure can be determined by adding it to the gauge pressure, i.e. P (abs) = P (atm) + P (gauge).
What are Flush Diaphragms and where are they used?
There are certain media which cannot be used with conventional pressure sensors due to it being either too viscous or requiring a high level of cleanliness.
In some test and research applications a sensor that changes the volume or shape of the vessel / pipe will lead to additional measurement uncertainties.
In some test and research applications a sensor that changes the volume or shape of the vessel / pipe will lead to additional measurement uncertainties.
Differential Pressure Sensor Frequently Asked Questions
A list of queries and explanations relating to the selection of specification parameters for differential pressure transducers and transmitters.
What is the Maximum Line Pressure?
This is the highest pressure that can be applied to both pressure connectors at the same time. If a differential pressure exists between two pressure connections, the total pressure on the high/positive side would be considered for the purposes of assessing line pressure. The line pressure is an indicator of the mechanical integrity of all materials, welds and seals used in the construction of the transmitter.
What is the Maximum Line Pressure?
This is the highest pressure that can be applied to both pressure connectors at the same time. If a differential pressure exists between two pressure connections, the total pressure on the high/positive side would be considered for the purposes of assessing line pressure. The line pressure is an indicator of the mechanical integrity of all materials, welds and seals used in the construction of the transmitter.
Measuring the Pressure of Hot Media
Installing pressure sensors close to high temperatures can lead to significant measurement errors and irreparable damage to the sensing elements and electronics.
The cheapest and simplest approach to protect a pressure sensor is to isolate it from the heat source. This can be done by extending the process connection with a short length of pipe and mounting the pressure sensor on the end instead.
The cheapest and simplest approach to protect a pressure sensor is to isolate it from the heat source. This can be done by extending the process connection with a short length of pipe and mounting the pressure sensor on the end instead.
Advantages of Stainless Steel Pressure Sensors
There are many types of materials used for constructing pressure sensors in a variety of applications, but those made from stainless steel are considered the most reliable and durable.
High Tensile strength
In hydraulic applications where pressure overloads are commonplace a stainless steel pressure sensor can withstand a high number of pressure cycles without fatigue damage.
High Tensile strength
In hydraulic applications where pressure overloads are commonplace a stainless steel pressure sensor can withstand a high number of pressure cycles without fatigue damage.
Are all IP68 Water Resistant Protection Ratings the same
It is often assumed that devices with an IP68 rating are suitable for immersing underwater for an indefinite period and any depth.
Not all devices that are IP68 are intended to be continuously submerged, some only require a temporary rating to protect from occasional submersion.
Not all devices that are IP68 are intended to be continuously submerged, some only require a temporary rating to protect from occasional submersion.
Make more use of Intelligent Pressure Gauge features and functions
Most uses for pressure gauges are as a simple indicator, but if you want to carry out additional operations an intelligent gauge opens up a wealth of functionality that will help you expand it's use in a variety of monitoring setups.
Changing Pressure Units
The most requested feature for digital pressure gauges is the ability to change pressure units and most gauges provide this function. Not all gauges will convert every pressure unit though, it can vary from a choice of just bar/psi, to many more, so it is worth checking the spec first to make sure all the units that you need to convert are included.
Max/Min Values
You can't always be present to check the pressure of a process, so how do you know whether the pressure has risen or fallen while you were away? A maximum/minimum or peak/valley hold feature would give you some idea of what has happened between visual checks. This feature will continually monitor the pressure and update the memory with the highest and lowest reading reached.
Changing Pressure Units
The most requested feature for digital pressure gauges is the ability to change pressure units and most gauges provide this function. Not all gauges will convert every pressure unit though, it can vary from a choice of just bar/psi, to many more, so it is worth checking the spec first to make sure all the units that you need to convert are included.
Max/Min Values
You can't always be present to check the pressure of a process, so how do you know whether the pressure has risen or fallen while you were away? A maximum/minimum or peak/valley hold feature would give you some idea of what has happened between visual checks. This feature will continually monitor the pressure and update the memory with the highest and lowest reading reached.
Is Measurement Resolution the same as Accuracy
You will find mentions of resolution and accuracy on many product information sheets for pressure measuring equipment, however when discussing the performance of equipment the two terms often get confused as meaning the same.
Resolution defines the ability to distinguish one reading from another. For a digital pressure gauge the resolution is normally referred to as the number of readable digits, e.g. 2 bar range with a 5 digit display would have a 0.1 mbar resolution.
Resolution defines the ability to distinguish one reading from another. For a digital pressure gauge the resolution is normally referred to as the number of readable digits, e.g. 2 bar range with a 5 digit display would have a 0.1 mbar resolution.
Using an Absolute Sensor to Measure Gauge Reference Pressure
When it is necessary to present gauge reference pressure data, an absolute pressure sensor can be used in some situations if a gauge pressure sensor is not available.
An absolute pressure sensor will measure total pressure independent of atmospheric pressure changes, unlike a gauge pressure sensor which measures pressure relative to atmospheric pressure. To convert the absolute reading to a gauge reference type the atmospheric pressure should be subtracted from the total measured pressure.
An absolute pressure sensor will measure total pressure independent of atmospheric pressure changes, unlike a gauge pressure sensor which measures pressure relative to atmospheric pressure. To convert the absolute reading to a gauge reference type the atmospheric pressure should be subtracted from the total measured pressure.
What to investigate before selecting an IP68 Pressure Transducer for measuring Liquid Level
To avoid fitting an unsuitable device or one that will not last a long time, it pays to consider all the factors that will influence the final specification you choose.
What type of liquid is to be measured?
This will help select a device with the most compatible construction materials. Submersible pressure sensors are comprised of sensing module, body, cable and seals, all of which must be compatible with the substance in which the sensor will be immersed.
What is the specific gravity or density of the liquid compared to freshwater?
The hydrostatic pressure generated by a fixed height of liquid is proportional to the specific gravity. 10 metres of water is a very close approximation to a 1 bar hydrostatic pressure, but if the specific gravity is say 0.9 of water (fresh water has a specific gravity of 1.0) a 10 metre head of this liquid would generate a 0.9 bar hydrostatic pressure instead. The output of some submersible pressure sensors can be scaled to correct for specific gravity without the need for the installer to compensate for it within the signal conditioning instrumentation.
What type of liquid is to be measured?
This will help select a device with the most compatible construction materials. Submersible pressure sensors are comprised of sensing module, body, cable and seals, all of which must be compatible with the substance in which the sensor will be immersed.
What is the specific gravity or density of the liquid compared to freshwater?
The hydrostatic pressure generated by a fixed height of liquid is proportional to the specific gravity. 10 metres of water is a very close approximation to a 1 bar hydrostatic pressure, but if the specific gravity is say 0.9 of water (fresh water has a specific gravity of 1.0) a 10 metre head of this liquid would generate a 0.9 bar hydrostatic pressure instead. The output of some submersible pressure sensors can be scaled to correct for specific gravity without the need for the installer to compensate for it within the signal conditioning instrumentation.
Determining the Signal Cable Length of a Suspended Liquid Level Transducer
Deciding the correct length of cable for a suspended IP68 transducer is an important part of specifying, if the cable is too short it is difficult and expensive to join two cables together and make the seal liquid tight.
There are two separate parts of the installation that need to be considered to determine the overal length which is the suspended length and any extra length that is needed to reach the termination point from the point of suspension.
There are two separate parts of the installation that need to be considered to determine the overal length which is the suspended length and any extra length that is needed to reach the termination point from the point of suspension.
Why are Submersible applications so demanding of Pressure Transducers?
Placing a sensing device in a liquid is one of the most hostile environments to ensure a long reliable service life.
The extra considerations for design engineers include:
The extra considerations for design engineers include:
- Keeping pressurised liquid out.
- Preventing condensation damage to the internal electronics.
- Corrosion protection for all the materials used in the transducer construction.
- Adequate protection from lightning surges in exposed installations.
There are many types of place where liquid level is measured such as Tanks, Reservoirs, Boreholes, wells, Rivers or Lakes, but the basic rules for the design of a submersible pressure transducer are the same for all of these situations.
Transforming a 2 wire Current Loop into a Voltage Output Signal
If you are running a signal cable over a long distance or have a spare current output pressure transmitter, it is possible to convert the output signal to a voltage type to make it compatible with voltage only input devices.
A typical current output is 2 wire 4 to 20 mA which is designed to be connected in a series with the power supply and other components included in the circuit. The pressure transmiitter acts as a current source regulating the current at a particular pressure for a range of load impedences as long as there is sufficient supply voltage to power it.
A typical current output is 2 wire 4 to 20 mA which is designed to be connected in a series with the power supply and other components included in the circuit. The pressure transmiitter acts as a current source regulating the current at a particular pressure for a range of load impedences as long as there is sufficient supply voltage to power it.
Does the type of Engineering Units matter for Pressure Transmitters
When selecting a part number for a pressure transmitter you will need to choose a pressure range. Usually a manufacturer will designate pressure ranges in the most common unit used by it's customers.
For the USA the most common unit is psi and for Europe it is bar, but what if you are working with other units such as kPa or inHg, is it possible to use a pressure transmitter scaled in bar or psi for other types of unit?
For the USA the most common unit is psi and for Europe it is bar, but what if you are working with other units such as kPa or inHg, is it possible to use a pressure transmitter scaled in bar or psi for other types of unit?
Considerations for monitoring Landfill Water Level
In recent years regulations for environmental control, health and safety issues have become much more stringent for existing and new landfill sites. The regulations encompass many considerations and some involve the measurement and control of water level in many positions around a waste disposal site.
One application is ensuring contaminated water is contained within a tanked zone and does not escape into the surrounding environment. Water level is also monitored at syphoning points where the contaminated water (Leachate) is removed for processing.
In locations where the leachate is pooled there will also be relatively high concentrations of volatile hydrocarbon gases expelled due to the decomposition process within the landfill. Due to the presence of flammable gases, areas within landfill sites are classed as hazardous zones. It is requirement that any measurement instrumentation that is to be located inside a hazardous zone, should be approved and installed to the appropriate ATEX classification for that area.
One application is ensuring contaminated water is contained within a tanked zone and does not escape into the surrounding environment. Water level is also monitored at syphoning points where the contaminated water (Leachate) is removed for processing.
In locations where the leachate is pooled there will also be relatively high concentrations of volatile hydrocarbon gases expelled due to the decomposition process within the landfill. Due to the presence of flammable gases, areas within landfill sites are classed as hazardous zones. It is requirement that any measurement instrumentation that is to be located inside a hazardous zone, should be approved and installed to the appropriate ATEX classification for that area.
Converting 4 to 20mA Linear Signal to Square Root Extraction Output
Some pressure measurements are used to indirectly derive another type of measurand. One of these is the Rate of Flow of a gas or liquid. The flow rate along a closed pipe is directly proportional to the square root of the pressure drop or differential pressure between two points.
Since the relationship is non-linear there is a greater change in flow at low pressures compared to higher ones. In order to optimise the resolution of flow measurement the output on some differential pressure transmitters can be altered so that it is directly proportional to the flow rate rather than the differential pressure.
Since the relationship is non-linear there is a greater change in flow at low pressures compared to higher ones. In order to optimise the resolution of flow measurement the output on some differential pressure transmitters can be altered so that it is directly proportional to the flow rate rather than the differential pressure.
How does changes in Local Gravity affect Hydrostatic Pressure
The value of hydrostatic pressure for a fixed height column of fluid is directly proportional to the gravitional strength at a particular geographical location.
Generally if the height above sea level is increased the hydrostatic pressure will decrease. Also since the world is wider at the equator than the poles the gravitional pull will increase as you move closer to either the north or south pole.
Generally if the height above sea level is increased the hydrostatic pressure will decrease. Also since the world is wider at the equator than the poles the gravitional pull will increase as you move closer to either the north or south pole.
Why is Temperature included in Height of Fluid pressure units
Pressure units which are related to the height of a liquid often include a reference temperature e.g. 50 mH2O @ 4degC.
The hydrostatic pressure of a fluid at a certain height is determined by the total height of fluid above that point. If the temperature of the liquid is increased it will expand in volume increasing the fluid level, however the hydrostatic pressure will remain the same. Therefore when quoting a pressure in terms of fluid level it is useful to know the temperature.
The hydrostatic pressure of a fluid at a certain height is determined by the total height of fluid above that point. If the temperature of the liquid is increased it will expand in volume increasing the fluid level, however the hydrostatic pressure will remain the same. Therefore when quoting a pressure in terms of fluid level it is useful to know the temperature.
The different ways of pressure sealing a BSP parallel thread
There are two distinct styles of seal typically used for pressure instrumentation with a BSP thread fitting.
Pressure connections which include the suffix EN 837 or DIN 16288 are sealed on the end of the thread with a small diameter O ring which is placed around the post protruding from the end of the thread. In the female mating part of the pressure connection there is a hole with sufficient diameter to locate the male end post without pinching the O ring.
Pressure connections which include the suffix EN 837 or DIN 16288 are sealed on the end of the thread with a small diameter O ring which is placed around the post protruding from the end of the thread. In the female mating part of the pressure connection there is a hole with sufficient diameter to locate the male end post without pinching the O ring.
How Gravity affects the performance of Pressure Transducers
Any pressure transducer which relies on a force collecting diaphragm for sensing pressure, will be sensitive to a change in orientation.
A pressure transducer diaphragm is designed to flex when a force is applied to it. If the diaphragm is orientated horizontally it will sag slightly under the force of its own weight. If the diaphragm is then flipped upside down it will sag in the opposite direction. The movement in the diaphragm will translate as a slight change in pressure when monitoring the output signal of the device.
A pressure transducer diaphragm is designed to flex when a force is applied to it. If the diaphragm is orientated horizontally it will sag slightly under the force of its own weight. If the diaphragm is then flipped upside down it will sag in the opposite direction. The movement in the diaphragm will translate as a slight change in pressure when monitoring the output signal of the device.
Selecting pressure instruments for multiple application requirements
Choosing a pressure instrument can be a complex operation particularly if there are many application requirements that have to be met.
Assigning products to different categories helps to home in on one critical requirement, but if you have more than one requirement it requires sifting through the individual product specifications assigned to that particular category to pull out the ones which satisfy all the requirements.
Assigning products to different categories helps to home in on one critical requirement, but if you have more than one requirement it requires sifting through the individual product specifications assigned to that particular category to pull out the ones which satisfy all the requirements.
Incompatible Pressure Sensor Specifications
We occasionally receive requests for combinations of pressure sensor features that are not practical to include in the same specification. Below is a list of the most requested parameter combinations that are declined including explanations.
Low Pressure Range with High Media Temperature - the thin and large diameter diaphragms used in the construction of low range pressure sensors are more sensitive to thermal expansion which significantly effects sensor performance.
Low Pressure Range with High Media Temperature - the thin and large diameter diaphragms used in the construction of low range pressure sensors are more sensitive to thermal expansion which significantly effects sensor performance.
What are the abbreviations added to the end of a pressure range description
There is a loose convention across manufacturers for designating the type of reference that a pressure sensing device has, which can be confusing if you are unfamiliar with specifying this often overlooked but critical specification parameter.
To help identify the reference of a particular pressure range found on a product label or technical data sheet a list of abbreviated suffixes is provided below.
Gauge - Measuring pressure with reference to atmospheric pressure, also referred to as Relative and Vented Gauge:
g, G, rel, REL, vg, VG
To help identify the reference of a particular pressure range found on a product label or technical data sheet a list of abbreviated suffixes is provided below.
Gauge - Measuring pressure with reference to atmospheric pressure, also referred to as Relative and Vented Gauge:
g, G, rel, REL, vg, VG
Measuring the difference in air pressure between rooms
Monitoring and controlling the pressure in a room is a critical parameter in many indoor environments where the climate must be maintained at a particular temperature, humidity and cleanliness/containment level
In hospital operating theatres, semiconductor manufacturing facilities, computer data centers and biochemical research laboratories, it is necessary to ensure either a slightly higher or lower air pressure to prevent a contaminated atmosphere leaking outside or a clean atmosphere becoming contaminated from outside air.
In hospital operating theatres, semiconductor manufacturing facilities, computer data centers and biochemical research laboratories, it is necessary to ensure either a slightly higher or lower air pressure to prevent a contaminated atmosphere leaking outside or a clean atmosphere becoming contaminated from outside air.
What are the different types of Stainless Steel used in Pressure Transducer design
Whilst examining the suitability of materials used in the construction of a pressure transducer you will notice that different grades of stainless steel are used for the parts exposed to the pressure media. The choice of which stainless steel to use in a design is dependent on the required material strength, toughness, ease of manufacture, and corrosion resistance.
Stainless steel is a family of corrosion resistant iron alloys which have a Chromium (Cr) content of at least 10.5%. When exposed to Oxygen (O) either in the atmosphere or process media a self passivation process forms a surface layer which is corrosion resistant. The passive surface layer will naturally maintain itself over the life of the material.
There are 5 main groups of stainless steel which are Ferritic, Martensitic, Austenitic, Duplex and Precipitation-Hardenable Martensitic.
Stainless steel is a family of corrosion resistant iron alloys which have a Chromium (Cr) content of at least 10.5%. When exposed to Oxygen (O) either in the atmosphere or process media a self passivation process forms a surface layer which is corrosion resistant. The passive surface layer will naturally maintain itself over the life of the material.
There are 5 main groups of stainless steel which are Ferritic, Martensitic, Austenitic, Duplex and Precipitation-Hardenable Martensitic.
Why some Pressure Sensing Devices require the selection of an Elastomer Seal
When selecting pressure sensor options, occasionally you will come across a choice of seal materials to choose depending on the sensor design.
An all welded construction provides a high integrity and homogeneous material design. The main disadvantages of this kind of sensor design is the lack of flexibility to customise for different applications, induced measurement errors from mechanical stresses caused by the welding process and higher manufacturing costs.
An all welded construction provides a high integrity and homogeneous material design. The main disadvantages of this kind of sensor design is the lack of flexibility to customise for different applications, induced measurement errors from mechanical stresses caused by the welding process and higher manufacturing costs.
Specifying a General Purpose Pressure Sensor
If you need a sensor to measure gas or liquid pressure in a factory or laboratory environment there are a few parameters that should be considered in order to determine whether a general purpose device is going to be suitable.
The pressure of a fluid or gas is transmitted in all directions equally and over large distances, it is possible to install a pressure sensor some distance away from the process being measured via some suitable pipework.
The pressure of a fluid or gas is transmitted in all directions equally and over large distances, it is possible to install a pressure sensor some distance away from the process being measured via some suitable pipework.
Does Precision mean the same as Accuracy for Pressure Measurement Devices?
These two terms are indistinguishable to many people, even the Oxford Dictionary gives "Very Accurate" as one of the definitions for "Precision". However, as pointed out in their use of "Precise" the two words have slightly different meanings which is particularly relevant to pressure measurement.
In the context of a pressure measurement device, precision refers to how well it provides repeatable and linear results with increasing or decreasing pressure over many cycles. It is therefore an indication of the quality of measurement technology utilised and is a major factor effecting the cost of an instrument.
In the context of a pressure measurement device, precision refers to how well it provides repeatable and linear results with increasing or decreasing pressure over many cycles. It is therefore an indication of the quality of measurement technology utilised and is a major factor effecting the cost of an instrument.
Calibration Hand Pump performance depends on test volume
Most air hand pumps that are designed to be used as pressure calibrators include a coarse pressure generator and a fine pressure adjuster. The effectiveness of both is dependent on the test volume connected to the pump. The coarse or main pressure generator is typically a piston and cylinder arrangement which is actuated either by a set of calipers, a plunger, or a lever. The coarse change in pressure is applied by compressing the air to a high level inside a small cylinder which is then released to the lower pressure test volume increasing the pressure upon each cycle of the pump.
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